Method and system for measurement of road profile

Abstract

Apparatus and method for use on a measurement vehicle to measure road surface profiles while correcting for surface slope (cross slope and/or grade). Transducers are mounted on the vehicle suspended mass for measuring distance to the road surface and acceleration normal to the road surface as the vehicle is propelled over the road surface. A third transducer is responsive to fixed increments of vehicle travel over the road surface. Surface profile is determined in the spatial domain over each successive incremental distance. Total acceleration of the vehicle in the direction of the slope is measured, from which acceleration due to vehicle motion is subtracted. Elevation is determined as a trigonometric function of slope, and corrections are implemented to the profile signals.

The invention claimed is: 
     
       1. In a method of measuring road surface profile which includes the steps of providing a vehicle having a suspended mass adapted to be propelled over a road surface, measuring distance from the suspended mass to the road surface as the vehicle is propelled over the road surface, determining acceleration of said suspended mass perpendicularly of the road surface as the vehicle is propelled over the road surface, and determining road surface profile as a combined function of said distance and acceleration, the improvement for measuring slope of said road surface in a slope direction comprising the steps of measuring total acceleration of said vehicle in said slope direction, measuring motion acceleration in said slope direction due to motion of said vehicle, and determining road surface slope in said direction as a function of a difference between said total acceleration and said motion acceleration.   
     
     
       2. The method set forth in claim 1 wherein said step of determining road profile includes the step of subjecting signals indicative of acceleration of said mass perpendicularly of the road surface to highpass filtering, and wherein said step of determining road surface slope includes the step of subjecting signals indicative of said difference to lowpass filtering complementary to said highpass filtering. 
     
     
       3. In a method of measuring road surface profile which includes the steps of providing a vehicle having a suspended mass adapted to be propelled over a road surface, measuring distance from the suspended mass to the road surface at each of two spaced locations on said vehicle as said vehicle is propelled over the road surface, determining acceleration of said suspended mass perpendicularly of the road surface at each of said locations on said vehicle as said vehicle is propelled over the road surface, and determining road profiles at said locations as respective functions of said distances and accelerations, the improvement for measuring slope of said road surface between said profiles comprising the steps of measuring total acceleration of said vehicle in a direction parallel to said road surface, measuring motion acceleration of said vehicle in said direction parallel to said road surface due solely to motion of said vehicle over said road surface, determining acceleration of said vehicle in said direction parallel to said road surface due solely to gravity as a function of a difference between said total acceleration and said motion acceleration, and determining slope of said road surface between said road profiles as a function of said acceleration difference.   
     
     
       4. The method set forth in claim 3 comprising the additional step of storing signals indicative of said road profiles and said slope. 
     
     
       5. The method set forth in claim 4 wherein said step of determining slope of said road surface profiles comprises the step of determining a difference in elevation of said road surface profiles as a function of said acceleration difference and distance between said locations on said vehicle. 
     
     
       6. The method set forth in claim 5 wherein said step of storing said slope comprises the step of combining said elevation difference with one of said road profiles. 
     
     
       7. Apparatus for measuring road surface profile comprising a measurement vehicle adapted to be propelled over a road surface whose profile is to be measured and including a suspended mass, means positioned at spaced locations on said vehicle with respect to the direction of vehicle travel over the road surface for determining road surface profile as respective combined functions of acceleration perpendicularly of the road surface and distance to the road surface at each said locations, and means for measuring slope of said road surface between said profiles comprising means for measuring total acceleration of said vehicle in a direction extending between said vehicle locations parallel to said road surface, means for measuring motion acceleration of said vehicle in said direction between said vehicle locations due to motion of said vehicle over said road surface, and means for determining slope of said road surface between said road profiles as a function of a difference between said total acceleration and said motion acceleration.   
     
     
       8. The apparatus set forth in claim 7 wherein said slope-measuring means further comprises means for determining absolute difference in elevation between said road profiles as a function of said acceleration difference and distance between said vehicle locations measured parallel to said surface. 
     
     
       9. The apparatus set forth in claim 8 further comprising means for recording said road profiles and said elevation difference as a function of distance along the road surface. 
     
     
       10. The apparatus set forth in claim 9 wherein said profile-determining means are positioned at spaced locations laterally of direction of vehicle travel, said slope-measuring means measuring cross-slope of the road surface between said road profiles. 
     
     
       11. The apparatus set forth in claim 10 comprising a transverse accelerometer for measuring said total acceleration, a yaw rate transducer for measuring angular velocity of inclination laterally of said direction of travel, and means for determining said motion acceleration as a function of yaw rate times vehicle velocity. 
     
     
       12. The apparatus set forth in claim 9 wherein said profile-determining means are positioned at spaced locations longitudinally of direction of vehicle travel, said slope-measuring means measuring grade of the road surface between said road profiles. 
     
     
       13. The apparatus set forth in claim 12 comprising a longitudinal accelerometer for measuring said total acceleration, and means for determining said motion acceleration as a function of longitudinal velocity of said vehicle.